The present invention relates to a casting shell or refractory mold and in particular to a casting shell formed by additive fabrication or three dimensional printing, the three dimensionally printable refractory material and a method of manufacturing the casting shell using such a material.
Current metal casting methods, such as investment casting include the initial steps of fashioning a pattern that may be made of a volatizable material such as wax or foam duplicating the desired cast part. The pattern is then encased in a shell material, for example, a liquid ceramic material which cures to form a layer of a ceramic shell around the sacrificial pattern. Through the repetition of adding additional layers, the ceramic shell becomes strong enough to withstand the heat and pressure of receiving molten metal therein. The shell material is then heated to melt and volatize the pattern leaving a hollow cavity corresponding to the pattern. Casting material, for example molten metal, may then be poured down into the cavity. When the casting material has hardened, the surrounding ceramic shell is removed from the cast part.
While the current metal casting method results in the formation of high quality castings, it is a time consuming process and often expensive. Accordingly, it is desirable to introduce a method of manufacturing casting shells, i.e. refractory molds, which require fewer fabrication steps. By way of reducing the number of fabrication steps, such a method of manufacturing a casting shell would also reduce the potential for either human or equipment errors that may otherwise occur.
With the improvement of additive fabrication techniques and hardware, it is possible to use a 3-D powder printer to create a ceramic refractory casting shell without the use of a sacrificial pattern and the repetitive layering and drying steps associated with traditional investment casting shell manufacturing. However, while the additive fabrication hardware has improved to allow for the 3-D printing of casting shells, prior attempts to do so have failed to provide a three dimensionally printable refractory material suited for manufacturing high quality casting shells. Accordingly, there remains a need for a refractory material that is capable of being three dimensionally printed into a functioning casting shell for the casting of materials such as molten metal.